Methods and compositions for patterning biological material on a substrate are described, including a method for ablating biomolecules on a substrate with a laser to form a pattern. Patterned substrates and applications thereof are also described.
Control of the position or distribution of biologically active molecules or biomolecules on a substrate is important for a wide range of scientific and technological applications. This controlled positioning has commonly become known as “patterning” of these molecules. For example, the patterning of DNA oligonucleotides on a glass substrate is used to make microarrays; similarly the patterning of proteins on a substrate is used to make protein arrays. These types of arrays have a range of analytical and diagnostic applications. In cell biology, substrates patterned with extracellular matrix proteins are used to control the shape, position and behavior of cells.
To pattern biologically active molecules, a wide range of methods have been developed. These methods can be divided into two classes: self-assembled patterning and directed patterning. In self-assembled patterning the physical chemical properties of a molecule or combination of molecules are exploited under specific conditions to produce distributions of molecules with known non-random organizational properties. For example, a self-assembled monolayer of alkanethiols on gold will often have a high degree of order that results from intermolecular interactions between the components of the molecules. This order is a pattern, and it in turn can be used to create patterns of other molecules. Also, colloidal particles adsorbed onto a surface can have varying degrees of order that can be used to create patterns.
In directed patterning, the position of molecules is controlled by information that is brought in from the outside, such as a mask or a template. Directed patterning methods can in turn be divided into two types: lithographic approaches and writing approaches. Lithographic approaches include methods where a physical template such as a mask or a mold is used to transfer a pattern to an object. Examples include conventional photolithography and microcontact printing. In contrast, writing approaches use a serial approach to transfer a pattern, typically from a computer-based representation such as a CAD (computer assisted design) drawing, to an object. Electron beam lithography, despite its name, is a writing approach, by the definition used here. In general, lithographic approaches are good for producing many copies of the same pattern; writing approaches are good for producing unique patterns for producing a large number of different patterns, or for changing patterns quickly.
As noted above, there are a wide range of applications for patterning proteins and other biomolecules. One area that has become increasingly important over the past decade is patterning of proteins for cell biological and related applications. In vitro cell culture was developed to facilitate the study of the biomedical and industrial uses of cells outside of an animal. During the last century cell culture techniques and materials have been refined to more accurately reflect the in vivo environment of the cells, to provide analytically and diagnostically informative responses from cells, and to more efficiently grow cells for research and industrial biomedical uses. One aspect of the cellular microenvironment that is not well-captured by traditional cell culture is the spatial heterogeneity of molecules in the extracellular environment. Molecules are not randomly arranged or uniformly arranged in the extracellular environment, and the spatial organization of the molecules influences cell structure and function.